The present invention relates, in general, to battery monitors and, more particularly, to apparatus for monitoring the status of one battery or a battery string under load.
Telephone systems are required by regulatory agencies to provide telephone service in the event of an electrical utility power outage for a predetermined period of time, such as eight hours, for example. Thus, while the telephone system is normally powered by the electric utility power, a backup battery system must be employed to provide the necessary emergency power.
The typical telephone system includes a large number of distributed telephone or cabinets or huts usually at widely spaced locations in metropolitan and rural areas. It is common to have a plurality of DC batteries connected in various serial and parallel arrangements or in so-called “strings”. Such battery strings are charged by a trickle charger for the electric utility power. However, the battery strings provide the necessary backup power during an electric utility power outage which switched on via a suitable power outage detection and switching circuit.
As such, while the batteries may sit idle under a state of trickle charge for a considerable amount of time, it is important that each battery be operative in the event of a random power outage.
Monitoring the status of each of a plurality of batteries in each widely spaced telephone cabinets or huts is a time consuming and expensive task. One problem is simply the widespread nature of the telephone cabinet. Particularly in rural areas, such cabinets can be spaced many miles apart thereby making frequent and easy battery condition tests difficult.
The battery strings contain a number of batteries to provide a typical forty-eight volt supply. Depending on the telephone network, two volt, four volt, six volt and twelve volt batteries may be connected in series or series/parallel arrangements to provide the necessary forty-eight voltage DC backup power supply. Such batteries must be tested on a periodic basis and while being charged so as not to render the backup power supply inoperative during the battery test.
It would be desirable to provide an improved battery monitoring apparatus and method which monitors the condition of each one or more batteries which may be under load.